Palmer amaranth regrowing from PPO herbicide application — now what?

• If the Palmer amaranth pressure is heavy in these cases, I typically advise folks to disk down and replant.
• However, it is now July 8 and it is really late to go this route.

By Larry Steckel, Tennessee Extension Weed Specialist | Jul 08, 2013

There have been a few calls over the past several days on soybean fields where either a fomesafen based herbicide, Ultra Blazer or Cobra has been applied on Palmer amaranth that was greater than 4-inches and now the Palmer is growing back.

The question that follows is “what can I do next to salvage these soybeans?”

For this simple question there is no good answer. Unfortunately, based on driving through Tennessee last week and looking at soybean fields, my guess is there will be more of these type questions.

If the Palmer amaranth pressure is heavy in these cases, I typically advise folks to disk down and replant. However, it is now July 8 and it is really late to go this route.

At this late date about the only option is to come back with another PPO herbicide like Ultra Blazer or Cobra. I do not recommend anymore fomesafen (Prefix, Flexstar, Reflex, Dawn, Rhythm, etc) based herbicides in these cases, as the plant back to corn and grain sorghum is 10 months and the plant back to wheat is 4 months.

Do not expect miracles with an application of Ultra Blazer or Cobra as most of this recovering Palmer will recover from those applications as well. However, it does knock them down again and make them a little less competitive. Be sure to use the top end of the rate of those particular herbicides and apply them with 1 percent MSO at a minimum of 15 GPA.

Other options to control this large regrowing Palmer may be less available, but they include trying to find a chopping crew, cultivation or running a hooded application.

In fields with more scattered population of Palmer, chopping crews are an option. However chopping crews can often be difficult to find.

Cultivation can be an effective option on our few acres of tilled soybeans and if one can access a cultivator. If the soybeans happen to be in 38-inch wide rows, a hooded application of Gramoxone Inteon plus metribuzin will control large Palmer between the rows and in our research has been a very effective option.